Impact line printers comprise a print hammer bank in which a plurality of hammer elements are arranged in a row along a print line. It is common for the hammer bank to have 132 print hammer elements spaced ten to the inch. For ease of assembly and repair, the hammer bank comprises plural hammer modules or subassemblies mounted on a frame which may be a single bar. For each hammer element, there is an electromagnetic actuator also mounted on the frame. The electromagnetic actuators are operatively connected to the hammer elements by slender push rods which are part of a connector subassembly comprising plural push rods supported by guide plates the connector subassemblies being mounted onto the hammer support frame. Each hammer subassembly comprises a plurality of hammer elements individually mounted on a common pivot pin held stationary by a hammer block. The hammer block commonly takes the form of a solid piece formed with integral fins or spacers which isolate the individual hammer elements from each other. The pivot pin passes through aligned holes in the spacers and holes in the hammer elements. This type of hammer unit construction may be seen in U.S. Pat. No. 3,241,480 as well as in several IBM Printers such as the 3203, 3211 and 4248 Printers. The hammer elements are operated in small angle oscillations on the pivot pin which oscillations cause rapid wear at the hammer element/pivot pin bearing interfaces unless lubricated.
Various lubrication systems have been designed to maintain the hammer/pivot pin bearing interfaces properly lubricated for longer periods of use. One passive lubrication system uses a porous sintered hammer block and spacers impregnated with a supply of lubricant. Lubricant is supplied by capillary flow of the lubricant from the spacers to the surface of the pivot pin in the vicinity of the hammer element/pivot pin interfaces. Such a lubrication system is described in U.S. Pat. No. 4,896,596. Such a lubrication system can also be seen in the IBM 4245 Printer. While the impregnated block contains a goodly supply of lubricant, it is not nearly enough for a long period of printer operation especially at high printer speeds. Therefore means have been provided for supplementing the lubricant in the sintered hammer blocks. In one lubrication system, the supplementary lubrication means takes the form of felt pads initially saturated with lubricant and placed in cavities within the sintered insert block. Lubricant is supplied to the sintered hammer block insert by capillary flow from the felt pads in the cavities. Such a system is described in U.S. Pat. No. 4,756,246. It has been found however, supplementary lubrication means formed of felt materials release the lubricant too rapidly, have inadequate capacity, need occasional and even frequent replacement or need periodic application of lubricant which is then transferred by capillary action to the sintered hammer support block.
In a dynamic lubrication system the supplementary lubrication means is a felt wick, one for each hammer block. The wicks are initially impregnated with lubricant and a portion placed in contact with an external surface of the hammer block. Another portion of the wicks overlays a perforated tube connected to a pump. The wicks are periodically wetted with metered amounts of lubricant supplied by the pump. Lubricant is distributed to the individual wicks of the plural hammer blocks by means of a tube having spaced perforations in contact the wicks. Such a dynamic system is used in the IBM 4248 Printer. While such a system assures lubrication over a longer period of printer life than the passive system using felt pads, the system is imprecise as to amount and distribution of lubricant and requires a larger number of parts and controls which add to printer cost. Additionally, the application of lubrication at specific sites determined by the location of the perforations in the tube tends to localize the lubrication such that some bearing interfaces may receive more or less lubrication than needed. There is also some difficulty in precisely determining the frequency or amount of lubricant to be applied due to the fact that variations in lubricating requirements of the individual hammers is not readily predictable.